Grab the air cleaner housing and shake it around. If this duplicates the sound, you might need a new support bracket and rubber support bushings.

Also, my opinion is that you should always replace "wear" components in a complete set. As in, pads for both front brakes at one time, ball joints upper and lower on both sides at one time, etc. What I am saying is that you should go ahead and replace the rubber mount block at the back of the transmission. This is generally considered part of the "engine mount" system.

Ken300D